A sample of KClO₃ is heated and decomposes to produce O₂ gas. Th e gas is collected by water displacement at 26 °C. Th e total volume of the collected gas is 229 mL at a pressure equal to the measured atmospheric pressure, 754 torr. How many moles of O₂ form?

Strategy

The collected gas is a mixture of O₂ and H₂O. Because we are interested in the amount of O₂, we must first determine the partial pressure of the O₂ gas, then use the ideal gas law to find the amount of O₂.